Float drilling platform or similar floating structure

ABSTRACT

A floating sea platform is disclosed wherein at least three main columns support a deck structure. Float devices attached to the free ends of the columns are selectively filled with water to regulate the submersible depth of the floats. Bracing structure between the columns and two bracing members joints are provided to insure structural rigidity while minimizing the stress effects of waves during towing operations and while the platform is stationary.

United States Patent 1 Wipkink et al.

[ 1 May 27, 1975 [54] FLOAT DRILLING PLATFORM OR 3,443,543 5/1969 Willm et al. .i ll4/.5 D SMILAR FLOATING STRUCTURE 3,507,239 4/l970 Wi kink et al. l |4/ 5 D [75] Inventors: Johannes Wipkink, Sassenheim;

Marinus Van Holst; Johan Gerhard Primary Examiner-Trygve M. Blix Wolters, both of Maassluis, all of Assistant Examiner-Gregory W. O'Connor Netherlands Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, [73] Assignees: lngenieursbureau Marcon (Marine Zmn and Macpeak Consultants) B.V.; Scheepsbouwbelangen B.V., both of The Hague, Netherlands [57] ABSTRACT [22] Filed: 1972 A floating sea platform is disclosed wherein at least [21] App]. No.1 246,371 three main columns support a deck structure. Float devices attached to the free ends of the columns are selectively filled with water to regulate the submersfi ible depth of the floats. Bracing structure between the i 5 R 43 columns and two bracing members joints are provided I 0 care 1 to insure structural rigidity while minimizing the stress effects of waves during towing operations and while References Cited the platform is stationary UNITED STATES PATENTS 7 Claims, 6 Drawing Figures 3,407,610 10/1968 Wolff 61/465 2l28$l93 22 212888 1491 832D11fil422292lx$ i9 21 I) ll llf ill! ills i-lm w29263$3433323l l 27 2923 Fig- .1

FLOAT DRILLING PLATFORM ()R SIMILAR FLOATING STRUCTURE This invention relates to a floating drilling platform or similar floating structure comprising more than three vertical columns extending downwardly from the platform and rigidly connected thereto. said columns at their lower ends having floaters with means to sub merge them by filling with water. and with a central joint structure between the columns. from which structure bracings extend both to upper and to lower points of the columns, the centrelines of said bracings converging approximately to one single point. no joints, each for several bracings. being provided in the vertical side faces of the platform through adjacent columns.

Such floating structures are known. eg. from US. Pat. No. 3.507.239 and corresponding British Pat. Specification No. l.2l lifl9l. In said prior art a structure is shown. in which the central joint of bracings is positioned at a considerable distance below the workdeck of the platform and preferably at the height of the upper edge of the floaters. so at the lower end of the columns. Substantially horizontal and inclined bracings extend from this joint to low and high points on the columns. In the deck structure a second. secondary joint may be provided, connected by a substantially vertical bracing to said first joint and from which secondary joint only deck girders extend to the columns.

It has appeared that this structure, although having considerable advantages. is liable to improvement with respect to the guiding ol' the forces and loads and the influence of water and waves.

To obtain such an improvement a structure as given in the preamble above is according to the invention characterized in that the central joint structure is provided substantially at the level of the deck of the platform. and that from said joint structure substantially horizontal bracings extend to the columns and moreover inclined bracings extend downwardly. without interruption. each to the lower end of a column.

This gives the following advantages with respect to the said known structure:

When being tugged the floating structure usually has the floaters floating on the water and thus only partly submerged and in such a condition the known structure will be subjected to considerable influence of the waves on the joint structure at its low level between the columns. as such joint structure should have considerable dimensions. When applying the invention this is avoided. and thus it is possible in bad weather to con' tinue tugging with the structure floating high on the water. Thus it is not so early necessary to ballast the floating structure to have it submerged to a considerable ex tent for further tugging. in which partially submerged condition there is much more tugging resistance.

Also when the floating structure is thus partially submerged, so in very bad weather during tugging. and al ways when the platform is in stationary position for its normal use such as for drilling. the influence of the waves is less. because they cannot reach the joint strueturc near the workdcck. [t is true that the forces by the waves exerted on the columns are in part transmitted to said connecting structure. but only indirectly through the bracings and thus they are damped out so that they only act on the joint structure after they are decreased and after shocks are flattened out.

The inclined bracings extending from the joint structure according to thc imcntion to the lower points of (ill the columns guide the loads from the workdeck in the central part between the columns with all heavy structures thereon, such as drilling rigs etc.. immediately from the joint structure to the proximity of the floaters and thus to the floating surfaces for the structure. so that the load on the columns is considerably decreased. It is true that said bracings are under compression. so that possible buckling should be taken into account. but it nevertheless appears easy to make them strong enough in this respect without becoming heavy and bulkyv Moreover the joint structure at a high level in the proximity of the deck can be controlled and maintained easily during long periods of operation at sea. which is impossible or much more difficult for a joint structure at a low level. which the waves can easily reach. Thus it is also possible to protect the high joint structure better against corrosion.

In a preferred further embodiment of the matter of the invention the said structure is characterized in that it has a second central joint structure substantially vertically below the said main central joint structure. said second central joint structure having exclusively a connection with bracings which extend substantially horizontally one to the lower end of each column. which second joint structure is connected by a substantially vertical bracing structure to the said central joint structure in the proximity of the deck. Said second joint structure thus only serves for the horizontal connection between the lower ends of the columns and thus needs not transmit very high forces, while only a small number of bracings has to be connected thereby. so that it is possible to make this secondary joint of small dimensions and of light weight, the small dimensions entraining that the influence of waves thereon is negligible.

Preferably a structure according to the invention is further characterized in that the central joint structure in the proximity of the deck is embodied as a joint core with connections for the substantially horizontal bracings and with downwardly extending inclined substan tially prismatic or frustopyramidal parts. which directly or through connected transition pieces extending from said parts and tapering away therefrom. or by both measures together, are connected to bracings in line with said parts, said bracings having a smaller transverse sectional area than said protruding parts at their end, which are most remote from said bracing and thus more close to the joint structure.

In some cases. however, another embodiment of the connecting structure is preferred. which is possible by the fact that it is positioned so high as not to be influenced by water and waves and which may have advantages for a better support of the workdeck with heavy parts thereon such as a drilling rig etc. over a larger area. Such other embodiment is characterized in that the central joint structure in the proximity of the deck is embodied as a horizontal box or annular hollow beam with a substantially rectangular cross-section.

Said annular box or hollow beam may be circular in a horizontal plane. but perferably it has a polygonal shape in a horizontal plane. preferably with straight parts without kinks between the points where the bracings are connected thereto. Thereby the forces are transmitted in the most favourable way between hollow beam or box and braeings.

If. as indicated above. a secondary central joint structure is applied at a low level. it is preferred. in case of such a high main central joint structure in the shape of an annular hollow beam or box near the workdeck to embody the vertical connection between said two joint structures as one or more bracings extending if desired in a somewhat inclined direction from the lower face of the hollow beam or box near the deck to said secondary joint structure.

The invention will now be explained in more detail with reference to the enclosed drawings giving by way of example only possible embodiments of the matter of the invention.

in said drawings;

PK]. 1 is a sideview of a structure according to the invention embodied as a floating drilling platform;

Fl(]. 2 is a view from above of this platform;

FIG. 3 is a vertical section and view of a central part thereof substantially along the line lll-lll in FIG. 2'.

FIG. 4 is a sideview of a drilling platform according to the invention in a different embodiment,

PK]. 5 is a view from above of the central part of the structure of FIG. 4'. and

FIG. 6 is a section and view in a vertical plane of the part of the structure of FIGS. 4 and 5 according to the line VlVl in FIG 5.

The floating platforms as shown in the drawings dc rive their buoyancy essentially from five floaters l of circular cross'section. each connected through conical transition parts 2 to a column 3 extending upwardly and having the same axis as its floater 1. Columns and floaters are positioned in the corners of a horizontal regular pentagon.

The columns 3 may extend downwardly into the floaters l and be connected to the plane bottom face thereof. so that in the floaters there is a suitable annular space for ballasting around said downward extension of the columns.

At the upper end of this structure a deck structure 5 is applied which has not been shown in detail and the contours of which are indicated by dot and dash lines in FIG. 2 between the horizontal deck bracings l6 and 20 to be described below. This structure may comprise one or more decks as is known as such. In a floating drilling platform there will often be three decks. for engine rooms. for storing materials and tools and for living. At 6 in FIG. 2 there may be arranged a drilling rig and at 7 there may be a higher deck. ifdesired protruding further outside the structure and intended to consti tute a landing platform for helicopters.

ln FIGS. 1. 2 and 3 a central joint structure 8 is provided. which geometrically consists of a central prismatic core 9 with a vertical axis. Said core is polygonal. so that each upstanding side face thereof is perpendicular to the axis ofa bracing 16 extending horizontally to one of the columns 3. hi the embodiment shown. in which the columns are positioned at the corners of a regular pentagon. the core 9 in horizontal section and view from above is also a regular pentagon. Each verti cal bordering face of said core 9 has two protruding parts it] and ll. which merge into one another vcrti cally and which constitute one unitary structure. and which has common vertical bordering faces 12. The core 9 need not be embodied as a separate body with its own closed faces vertically. but may constitute an unitary structure with the parts It) and ll. which internallv is mainly open and hollow although ha ing reinforcing struts. baffles or the like internally. Such reinforcement may be plates welded internally in the core (ill and transmitting the forces in the desired directions. Moreover. there may be external reinforcements be tween the faces 12. As appears from FlU. 2 there are each time two vertical bordering faces 12 extending from the centre of the joint outwardly in parallel. although it is also possible that they converge somewhat outwardly. The upper bordering faces 13 and the lower bordering faces of the protruding parts ll are also parallel. but these may also if desired converge somewhat outwardly. so that the protruding parts ll may have a pyramidal shape. The upper bordering faces 13 and lower bordering faces could also have a different angle ofconverging than the vertical side faces 12. At the end faces 15 of the protruding parts ll their cross-sectional shape is a regular polygon. in this case a square.

Rectangular horizontal bracings 16 extend horizontally along the lower face of the deck from the protrud ing parts It) to the columns 3. lnclined bracings 22 with circular or other round crosssection extend from and with their axes each coinciding with an axis of a pro truding part 11 downwardly to the lower ends of the columns. Fora good connection of the protruding parts It to said bracings 22 each side of the square end face of a part 11 merges into a plane face part l7. which ter min-ates at I8 in the bracing 22 of cur ed or circular cross-section. and between said four plane faces 17 there are four conical faces 14 for each protruding part ll. If such conical faces are embodied as parts of cones with inclined axes and with circular base [if the bracings 22 are circular in cross-section) each having their apex in a corner of the square at the end a protruding part H. The plane faces [7 and the conical faces 14 have straight bordering lines between them. so that the faces [7 are triangles. This gives a simple possibillity of manufacturing and welding. as the plates. from which this structure is composed. will not have bordering lines in the shape of curved sections of cones.

The bracings 22 in the proximity of the columns 3 merge through transition parts 23 similar to the parts l4. l7 and having with four plane faces similar to faces 17 and four curved faces similar to faces 14 into mainly prismatic or pyramidal parts 24 by which they are each connected to their column 3. ()f the four bordering faces of the parts 24 the two vertical faces may be mutually parallel and the upper and lower face may also be parallel. to obtain prismatic connecting parts 24. but. if desired. it is possible to have two of said faces. oppositely. or each two pairs of said faces. di erge mutually to constitute a frustopyramidal part or the like. connected to the column by a larger cross-sectional area than the area by which it merges into the bracing 22 through the said alternating plane and cur cd surfaces.

lt appears from FIG. 2 that bracings l9 and 20 in the same horizontal plane as the bracings l6 connect the columns 3 mutually. In FIG. 1 the front bracing I) is shown as being broken away in the central part. to show the joint 8. The bracings Zll are rectangular. as well as the bracings l6. and the three bracings l) are circular in cross-section. with about frustoprismatic transition parts 2! at the columns. the upper face of which is hori/ontal and the two upstanding side faces thereof being vertical. the lower face extending dowrr \vardly to the column as appears clearly from Fl(i 1. Such connecting parts 21 merge through circumferentially alternating triangular plane and inclined conical plates at 28 into the bracings 19. In tllc proximity ofthe transition between conical parts 2 and columns 3 there is also each time in each plane through the axes of two adjacent columns a bracing 26 which extends horizontally between two adjacent columns. and a bracing 27. which extends in the same vertical plane through two adjacent columns 3 and upwardly to the proximity of a horizontal bracing I9, in the upper zone of the structure. All said bracings are preferably circular and have at both ends essentially prismatic or pyramidal connecting parts 30 which merge through four plane faces alternated by four conical faces at 29 into the circular bracings 26. 27.

From the lower face of the prismatic core 9 of joint 8 a circular bracing 3I extends vertically downwardly. which bracing at its upper end and lower end merges through a transition part 32. having also alternately a plane and a curved face. on the one hand into said core 9 and on the other hand into ajoint 33, which is pentagonal and prismatic in shape. and merges through transition parts 34. into five horizontal bracings 36. one to each column. This lower joint in a view from above has the same essential appearance as joint 8 (vide FIG. I). but it is much more simple as no inclined bracings are connected thereto. so that it is also. as seen in FIG. I. much lower in a vertical direction and thus it will have little resistance in the water. The transition pieces 32 each of course have not four but live plane triangular faces. alternated by five conical faces.

All bracings are hollow. with if desired the necessary reinforcements therein. such as baffles. ribs or frame parts.

In FIGS. 4. 5 and 6 an embodiment has been shown in which the central joint of FIGS. 1 and 2 is replaced by an annular body 36. assembled from flat plates to form a hollow beam. As appears from FIG. 5 this beam 36 is essentially pentagonal. with at the connections of the bracings l6 and 22. and thus in the corners of the pentagon. parts 37. which are perpendicular to the bisecting line of the live corner angles of the pentagon. so that the pentagon in said corners is as it were flattened and thus an irregular decagonal figure is obtained. Thus the forces are transmitted adequately in said corners between bracings and annular hollow beam 36.

The bracings 22 have connecting parts 38 to the hollow beam 36. which are also the connecting parts for the bracings I6. Thus the axes of the inclined bracings 22 do not intersect one another in the intersecting point of the axis of the horizontal bracings 16. as in the previous embodiment. but above the deck 5.

This structure gives a simplification of the support of the deck structure as this is now adapted to be supported over a large area and very efficiently by the hollow beam 36.

In this case a bracing 39 extends from said hollow beam 36 in a downward but somewhat inclined direction to the simple lower joint 40. The bracing 3) merges. as appears from FIG. 4. into the annular hollow beam 36 in a straight part in the lower face thereof between two parts 37. This bracing 39 in essence has the same transitions with alternating plane and curved faces. hcrc indicated by 41. to prismatic connecting parts 42 at the ends by which it is connected at its upper end to hollow beam 36 and at its lower end to joint 40. The bracings I6 and 22 could also merge into the hollow beam 36 by connecting parts tapering horizontally so as to be much broader at the hollow beam 36 than at the bracing. in which case such bracings would preferably not be connected to the corners of the pentagonal hollow beam. but to the central parts of the sides thereof.

The hollow beam 36 may be replaced by a hollow box having the same outer configuration but being fully closed in its horizontal upper and lower face.

What we claim is:

1. In a floating platform for the open sea of the type including a number of vertical columns carried by floating devices at their lower ends. the floating devices having a larger horizontal cross-sectional area than the columns, a horizontal work deck carried by said columns. and a plurality of horizontal and/or inclined bracing members between adjacent columns to maintain the relative position of the columns. the improve ment comprising:

a. a first bracing member joint centrally located between all of the columns adjacent the lower surface of the horizontal work deck.

b. a second bracing member joint substantially vertically below said first bracing member joint,

c. a plurality of bracing members emanating from said first bracing member joint to upper and lower points on said columns. wherein the bracing members between the first bracing member joint and the upper points on said columns lie in on plane. the first bracing memberjoint having a central core member having a polyhedral shape with the number of faces corresponding to the number of bracing members leading to said joint. a first connecting portion protruding horizontally from said core member. the number corresponding to the number of bracing members extending from said joint to said lower points on said columns. and third connecting portions extending downwardly toward said second bracing member joint. and

d. a plurality of bracing members emanating from said second bracing member joint only to lower points on said columns. and to said first joint.

2. The improved floating platform of claim I wherein said second connecting portions are substantially prismatic or frustopyramidal in shape.

3. The improved floating platform of claim 1 wherein said central core member comprises a hollow closed section beam.

4. The improved floating platform of claim 3 wherein said beam is formed in the shape of a polygon.

5. The improved floating platform of claim 4 wherein said first connecting portions protrude from the apexes of said polygonal beam.

6. The improved floating platform ofclaim I wherein said second bracing member joint comprises a. a central core member having a polyhedral shape with the number of faces corresponding to the number of bracing members extending from said joint to said lower points on said columns.

b. first connecting portions protruding horizontally from said core member. the number corresponding to the number of bracing members extending from said joint to said lower points on said columns. and

c. second connecting portions protruding vertically from said core member toward said first joint.

7. The improved floating platform of claim 4 wherein said second joint comprises:

a. a central core member having a polyhedral shape with the number of faces corresponding to the 7 8 number of bracing members extending from said said joint to said lower points on said columns. and 1 Smd lower Pomts columns c. second connecting portions protruding vertically b, first connecting portions protruding horizontally from said core member. the number corresponding to the number of bracing members extending from from said core member toward said first joint (ill 

1. In a floating platform for the open sea of the type including a number of vertical columns carried by floating devices at their lower ends, the floating devices having a larger horizontal cross-sectional area than the columns, a horizontal work deck carried by said columns, and a plurality of horizontal and/or inclined bracing members between adjacent columns to maintain the relative position of the columns, the improvement comprising: a. a first bracing member joint centrally located between all of the columns adjacent the lower surface of the horizontal work deck, b. a second bracing member joint substantially vertically below said first bracing member joint, c. a plurality of bracing members emanating from said first bracing member joint to upper and lower points on said columns, wherein the bracing members between the first bracing member joint and the upper points on said columns lie in on plane, the first bracing member joint having a central core member having a polyhedral shape witH the number of faces corresponding to the number of bracing members leading to said joint, a first connecting portion protruding horizontally from said core member, the number corresponding to the number of bracing members extending from said joint to said lower points on said columns, and third connecting portions extending downwardly toward said second bracing member joint, and d. a plurality of bracing members emanating from said second bracing member joint only to lower points on said columns, and to said first joint.
 2. The improved floating platform of claim 1 wherein said second connecting portions are substantially prismatic or frustopyramidal in shape.
 3. The improved floating platform of claim 1 wherein said central core member comprises a hollow closed section beam.
 4. The improved floating platform of claim 3 wherein said beam is formed in the shape of a polygon.
 5. The improved floating platform of claim 4 wherein said first connecting portions protrude from the apexes of said polygonal beam.
 6. The improved floating platform of claim 1 wherein said second bracing member joint comprises a. a central core member having a polyhedral shape with the number of faces corresponding to the number of bracing members extending from said joint to said lower points on said columns, b. first connecting portions protruding horizontally from said core member, the number corresponding to the number of bracing members extending from said joint to said lower points on said columns, and c. second connecting portions protruding vertically from said core member toward said first joint.
 7. The improved floating platform of claim 4 wherein said second joint comprises: a. a central core member having a polyhedral shape with the number of faces corresponding to the number of bracing members extending from said joint to said lower points on said columns, b. first connecting portions protruding horizontally from said core member, the number corresponding to the number of bracing members extending from said joint to said lower points on said columns, and c. second connecting portions protruding vertically from said core member toward said first joint. 